Apparatus and method for the treatment of biosolids

ABSTRACT

Biosolids in the nature of sewage sludge is processed in a controlled environment to produce a dried sludge product of relatively high dry solid content with the elimination of or reduced levels of pathogens. The water containing sewage sludge is dried while cascading within a processing chamber using heated air at a temperature below the ignition or smoldering temperature of the sewage sludge to prevent the formation of embers. The sewage sludge before discharge is retained within the processing chamber for a sufficient time and temperature as mandated by the Environment Protection Agency rules and guidelines.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional, of U.S. patent application Ser.No. 13/900,167 filed May 22, 2013, which is a divisional of U.S. patentapplication Ser. No. 13/480,732 filed May 25, 2012, the disclosures ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates in general to an apparatus and method forthe treatment of biosolids, and more particularly, to an apparatus andmethod for the reduction and/or destruction of pathogens in sewagesludge to reduce health risks to humans and animals associated with thedisposal of dried sewage sludge.

BACKGROUND OF THE INVENTION

Sewage sludge also known as biosolids is a solid, semi-solid, or liquidresidue generated during the treatment of domestic sewage in specialtreatment devices. Sewage sludge includes, but is not limited to,domestic septage; scum or solids removed in primary, secondary, oradvanced waste water processes; and a material derived from sewagesludge. Sewage sludge does not generally include ash generated duringthe firing of sewage sludge in a sewage sludge incinerator or grit andscreenings generated during preliminary treatment of domestic sewagesludge in the treatment device.

Domestic septage is either liquid or solid material removed from aseptic tank, cesspool, portable toilet, Type III Marine sanitationdevice, or similar treatment device that receives only domestic sewage.Domestic septage does not generally include liquid or solid materialremoved from a septic tank, cesspool, or similar treatment device thatreceive either commercial waste water or industrial waste water, anddoes not generally include grease removed from a grease trap at arestaurant. Domestic sewage is generally waste and waste water fromhumans or household operations that is discharged to or otherwise entersa treatment device.

Sewage sludge treatment has been known to include three basic processes:preliminary treatment, primary settlement, and secondary treatment.Preliminary treatment involves grit removal and screening to removelarger material such as rags, towels, etc. In primary settlement, thesewage sludge flows through large tanks where smaller organic materialis allowed to drop out. During the secondary treatment stage, the mixedliquor is aerated to aid bacteria in breaking down its mass, after whichthe resulting secondary sludge is allowed to settle. The sludge producedby the primary settlement process and the secondary oxidation process iscombined to form the untreated sludge often known as raw sludge. Thisraw sludge can then be fed directly to a dryer or to a digester forfurther digestion by anaerobic or aerobic bacteria after which it can befed to a dryer. Prior to drying the raw sludge is dewatered. Free wateris removed by mechanical means such as a belt press or centrifuge toachieve around 30% dry solids. The material produced is referred to assludge cake, which may be stored for later transportation to anothersite for drying. The sludge now passes to a dryer for removal of theremaining water to produce the finished product, normally 90-95% drysolids.

Drying can be accomplished either by convection drying when hot gas/airis blown through or over the sewage sludge or by conduction dryingwhereby the sewage sludge is brought into contact with a heated surface.In the case of convection drying, the gas (air) flowing through thedryer can be heated directly or indirectly. With direct heating, the hotwaste gas (oxygen depleted) from a combustion chamber is fed into thedryer, while with indirect heating, air is heated via a heat exchanger.With conduction drying, heat is usually provided by either steam or froma hot oil system. The dryer can have various combinations of heatedjackets and hollow paddles/discs through which the heating medium flows.There are various types of known thermal dryers such as: (1) horizontaldrum dryers (e.g., rotary dryers, paddle dryers, and thin film dryers);(2) vertical tray dryer-pelletizers; (3) conveyor belt dryers; and (4)fluidized bed dryers.

Sewage sludge is known to contain pathogens which are disease causingorganisms such as certain bacteria, viruses, and parasites. Thesepathogens when present in the dried sewage sludge may be dangerous tohumans and other animal life. Sewage sludge often attracts rodents,flies, mosquitoes, or other organisms capable of transporting infectiousagents.

In 1993, the U.S. Environmental Protection Agency (EPA) promulgatedrules to ensure public safety in the treatment and handling of sewagesludge. In particular, the EPA issued rules known as “Part 053 Rule” anddescribed in EPA publications EPA/625/R-92/013 (December 1992) andentitled “Control of Pathogens and Vector Attractions in Sewage Sludge”;EPA/832-B-92-005 entitled “Domestic Septage Regulatory Guidance: A Guideto the EPA 503 Rule,” and EPA/832/R-93/003 (September 1994) entitled “APlain English Guide to the EPA Part 503 Biosolids Rule.” Particularly,Chapter 5 of EPA/832/R-93/003 entitled “Pathogen and Vector AttractionReduction Requirements” addresses treatment of biosolids to addresspathogens.

Accordingly, despite the known drying equipment and methods fortreatment of pathogen containing sewage sludge, there remains the needfor improvements, for example, an apparatus and method which enables theprocessing of pathogen containing sewage sludge under the EPA Rules andguidelines.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the invention, there is disclosedan apparatus for the treatment of sewage sludge, comprising: a housinghaving a sidewall forming a processing chamber; a plurality ofvertically spaced apart supports for receiving sewage sludge cascadingthrough the processing chamber; a source of heated gas in communicationwith the processing chamber for treatment of the sewage sludge cascadingthrough the processing chambers; and a manifold coupled to the sidewallfor supplying the heated gas to a plurality of locations within theprocessing chamber, the manifold including an elongated openingconfigured for discharging the heated gas into the processing chamber,and at least one barrier partially obstructing the discharging of theheated gas from the opening into the processing chamber.

In accordance with another embodiment of the invention, there isdisclosed an apparatus for the treatment of sewage sludge, comprising: ahousing having a sidewall forming a processing chamber having an upperportion and a lower portion, the housing having a diameter; a pluralityof vertically spaced apart trays arranged within the upper and lowerportions of the processing chamber for receiving sewage sludge cascadingthrough the processing chamber; a source of heated gas in communicationwith the upper and lower portions for the treatment of sewage sludgewithin the plurality of trays; a manifold coupled to the sidewall forsupplying the heat gas to the upper and lower portions of the processingchamber, the manifold including an elongated opening configured fordischarging heated gas into the upper and lower portions in a directiontransverse to the diameter of the housing, and at least one barrierwithin the opening for partially obstructing the discharging of heatedgas from the opening into the processing chamber; and an outlet forexiting exhaust gas from within the upper and lower portions formedwhile treating the sewage sludge therein.

In accordance with yet another embodiment of the invention, there isdisclosed an apparatus for the treatment of sewage sludge containing apathogen, comprising: a housing including a sidewall having an innersurface forming a processing chamber having an upper portion and a lowerportion, the housing having a diameter; a plurality of vertically spacedapart rotatable trays arranged within the upper and lower portions ofthe processing chamber for receiving sewage sludge cascading through theprocessing chamber; a source of heated air in communication with theupper and lower portions for the treatment of sewage sludge within theplurality of trays; a manifold coupled to the sidewall for supplying theheat air to the upper and lower portions of the processing chamber, themanifold including an elongated opening configured for dischargingheated air into the upper and lower portions in a direction parallel tothe inner surface of the sidewall and perpendicular to the diameter ofthe housing, and at least one barrier within the opening for partiallyobstructing the discharge of heated air from the opening into theprocessing chamber; at least one leveler associated with one of thesupports for leveling sewage sludge received therein, wherein thebarrier is arranged in alignment with the at least one leveler; anoutlet for exiting water vapor from within the upper and lower portionsformed while treating the sewage sludge therein, and a controller forcontrolling the temperature of the heated air below the ignition orsmoldering temperature of the sewage sludge.

In accordance with yet still another embodiment of the invention, thereis disclosed a method for treatment of sewage sludge containing apathogen, comprising: cascading sewage sludge containing water and atleast one pathogen between a plurality of vertically spaced apartsupports within a processing chamber; heating the sewage sludge whilecascading within the processing chamber to remove a portion of the waterwithin the sewage sludge thereby forming a reduced water content sewagesludge; heating the reduced water content sewage sludge for a sufficienttime and at a sufficient temperature to reduce the amount of the atleast one pathogen within the sewage sludge thereby forming a treatedsewage sludge; supplying heated gas to the processing chamber forheating the sewage sludge for removing a portion of the contained watertherein and for reducing the amount of the at least one pathogen withthe sewage sludge; and controlling the temperature of the heated gaswithin the processing chamber below the ignition temperature of thesewage sludge to prevent the formation of embers therefrom.

In accordance with yet still another embodiment of the invention, thereis disclosed a method for treatment of sewage sludge containing apathogen, comprising: cascading sewage sludge containing water and atleast one pathogen between a plurality of supports vertically stackedwithin an upper portion and a lower portion of a processing chamber;heating the sewage sludge while cascading between the supports withinthe upper portion of the processing chamber to remove a portion of thewater within the sewage sludge thereby forming a reduced water contentsewage sludge; heating the reduced water content sewage sludge withinthe lower portion of the processing chamber for a sufficient time and ata sufficient temperature to reduce the amount of the at least onepathogen thereby forming a treated sewage sludge; exiting exhaust gascreated in the upper and lower portions of the processing chamber;recycling at least a portion of the exhaust gas to the processingchamber for heating the sewage sludge contained therein; supplyingheated gas to the upper portion of the processing chamber for removing aportion of the water contained within the sewage sludge and to the lowerportion of the processing chamber for reducing the amount of the atleast one pathogen within the sewage sludge; and controlling thetemperature of the heated gas within the processing chamber below theignition temperature of the sewage sludge to prevent the formation ofembers therefrom.

In accordance with yet still another embodiment of the invention, thereis disclosed a method for treatment of sewage sludge containing apathogen, comprising: cascading sewage sludge containing water and atleast one pathogen between a plurality of vertically spaced apartsupports within a processing chamber; heating the sewage sludge whilecascading within the processing chamber to remove a portion of the waterwithin the sewage sludge thereby forming a reduced water content sewagesludge of at least 90% dry solids; heating the reduced water contentsewage sludge at a temperature at least in the range of 50° C. 80° C.and for 20-30 minutes to reduce the amount of the at least one pathogenwithin the sewage sludge thereby forming a treated sewage sludge;supplying heated air to the processing chamber in the temperature rangeof 120° C. 175° C. for heating the sewage sludge for removing a portionof the contained water therein; controlling the temperature of theheated air within the processing chamber below the ignition temperatureof the sewage sludge to prevent the formation of embers therefrom; andwherein supplying the heated air to the processing chamber furthercomprises discharging the air into the processing chamber in a directionperpendicular to a diameter of a housing providing the processingchamber.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with features, objects and advantages thereof may best beunderstood by reference to the following detailed description when readwith the accompanying drawings in which:

FIG. 1 is a perspective view, with partial cutaway, of an apparatus forthe treatment of sewage sludge in accordance with one embodiment of thepresent invention.

FIG. 2 is a diagrammatic cross-sectional illustration of the apparatusas shown in FIG. 1.

FIG. 3 is a perspective view of a hot gas distribution manifoldconstructed in accordance with one embodiment of the present invention.

FIG. 4 is a diagrammatic illustration of an apparatus for treatment ofsewage sludge in accordance with another embodiment of the presentinvention.

FIG. 5 is a diagrammatic illustration of an apparatus for treatment ofsewage sludge in accordance with still another embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In describing the preferred embodiments of the invention illustrated inthe drawings, specific terminology will be used for the sake of clarity.However, the invention is not intended to be limited to the specificterms so used, and it is to be understood that each specific termincludes all equivalence that operate in a similar manner to accomplisha similar purpose.

Referring now to the drawings, wherein like reference numerals representlike elements, there is shown in FIGS. 1 and 2 an apparatus 100constructed for the treatment of sewage sludge in accordance with oneembodiment of the present invention. The apparatus 100 processes sewagesludge containing various amounts of water to produce a dried biosolidmaterial having a pathogen content within the EPA guidelines, whileeffectively eliminating dust fumes and odor during operation therebyproducing a dried granular product with no detectable odor.

As shown, a hollow housing 102 forms an internal central processingchamber 104. The housing 102, which may be cylindrical or polygonal orrectangular is constructed from one or more sidewalls 106 which extendaround the circumference of the chamber 104, a top wall 108 and a bottomwall 110. The chamber 104 is provided with a plurality of adjacentprocessing zones extending generally continuously from the top wall 108to the bottom wall 110, whereby processing of the sewage sludge takesplace simultaneously at each of the plurality of treatment zones.

The apparatus 100 may include a variety of types of components fortransferring the sewage sludge through the different zones. For example,the apparatus may incorporate a plurality of vertically stacked spacedapart material supports such as trays 112. According to one embodiment,the trays 112 may be divided into one or more segments 114 by means ofelongated radially spaced apart openings 116 within the trays. In thepreferred embodiment, the trays 112 are formed as an annular shapedstructure. The openings 116 allow sewage sludge to pass from one tray toan underlying lower tray in a cascading fashion. For example, the trays112 may be attached to a rotating structure, and thus may rotate about asubstantially vertical axis as the structure rotates. As a result, thesewage sludge will cascade downwardly through the processing chamber 104from tray to tray.

Cantilever devices such as wipers 118 are optionally arranged extendingover the trays 112 to push sewage sludge from the trays through theopenings 116 as the trays rotate. Alternatively, the trays 112 mayremain stationary, and the wipers 118 may sweep across the trays todischarge the sewage sludge thereon. Accordingly, sewage sludge istransferred from the topmost tray 112 within the processing chamber 104through the plurality of vertically stacked trays to the lowermost traywithin the chamber for ultimate discharge from the apparatus 100. Inaccordance with one embodiment, each tray 112 may be provided with aplurality of wipers 118 overlying each tray, particularly where thereare a plurality of tray openings 116.

The sewage sludge to be processed is supplied to at least one materialinlet 120 provided within the top wall 108. The inlet 120 is arrangedoverlying the topmost tray 112 for distributing the sewage sludge ontothe tray. Any number of inlets 120 may be provided for simultaneouslyfeeding sewage sludge into the apparatus 100 for processing. One or morematerial outlets 122 are provided on the bottom wall 110 for dischargingprocessed sewage sludge from the last most tray 112 in the apparatus100. Accordingly, any number of material inlets 120 and any number ofmaterial outlets 122 may be provided for feeding the sewage sludge to beprocessed into the chamber 104 and for discharging processed materialthereform.

Referring to FIG. 2, there is illustrated in different detail theconstruction of the apparatus 100 in accordance with one embodiment ofthe present invention. Inside the processing chamber 104, the apparatus100 incorporates the plurality of annular shaped trays 112 arranged onedisposed over the other in a vertical stack. This allows the sewagesludge to cascade downwardly with the processing chamber 104 from onetray 112 to the next tray. The trays 112 surround a plurality ofvertically aligned fans 124, as to be described hereinafter, attached toa common central fan shaft 126. The fans 124 circulate the atmosphere orenvironment inside the chamber 104 and over the sewage sludge on thetrays 112. Each fan 124 typically covers several trays 112, for example,often trays 6-8, thereby defining one or more processing zones with theapparatus 100.

The sewage sludge to be processed is received on the topmost tray 112and progressively transferred to the lowermost tray in a cascadingfashion. In one embodiment, the sewage sludge may cascade along a linearor spiral path within the processing chamber 104. Each tray 112 may beconnected to at least one stanchion 128, wherein several stanchions arepositioned around the fan shaft 126, thereby forming a squirrel typecage. Coupled to the stanchions 128 is a turntable 130 at the lower endof the chamber 104. According to one embodiment, the turntable 130 isconnected to the rotatable cage structure which surrounds the fan shaft126. At least one drive assembly 132 including a plurality of gearscauses the turntable 130 to rotate, thereby causing the stanchions 128and the trays 112 to revolve.

Referring to FIG. 1, the trays 112 are generally planar in nature havingan annular shape provided by a central opening 134. In the preferredembodiment, the trays 112 include a single radially extending slot likeopenings 116. The opening 116 is sized to permit the sewage sludge beingprocessed on the tray 112 to be discharged therefrom as to be describedhereinafter. In other embodiments, it is contemplated that each tray 112can be divided into any number of tray segments by including a pluralityof radially extending slot-like openings 116. The construction of such atray 112 is disclosed in co-pending application Ser. No. 13/183,671entitled “Multi-Stream Material Processing Apparatus,” the disclosure ofwhich is incorporated herein by reference.

The outer and inner circumferential edges of the trays 112 are providedwith a raised lip 136 dimensioned in height so that each of the trayswill contain a volume and layer thickness of sewage sludge beingprocessed. The specific height of each lip 136 is generally dependentupon the particular nature of the sewage sludge being processed. Thus,in cases where thin layers of sewage sludge are desired, the height ofthe lips 136 will be relatively shallow. In the alternative, wherethicker layers of sewage sludge are to be processed, the height of thelips 136 will be greater. Accordingly, the thickness of the sewagesludge to be processed can be varied in the apparatus.

A rigidly mounted leveler 138 is optionally provided assembled adjacenteach tray 112 to brush across the top surface of the sewage sludgeplaced on the tray, thereby leveling the material and exposing materialunderneath the top portion to the environment within the chamber 104.Any number of levelers 138 may be positioned circumferentially aroundthe trays 112. It is not required that every tray 112 have a leveler138. For example, the first few trays where the sewage sludge issomewhat pasty, levelers might not be provided. Sewerage sludge that maybe spilled by the wipers 118 or levelers 138 over the sides of the trays112 fall onto an optionally provided catch plate (not shown). The catchplate, if provided, is angularly positioned with respect to the trays112 to cause sewage sludge which is spilled off of a tray above to fallonto the catch plate and be directed onto a tray below. In this manner,the sewage being processed in the chamber 104 cascades downwardly fromthe upper tray 112 to a lower tray.

As the sewage sludge is being moved through the chamber 104 as thus fardescribed, further elements may be implemented within the chamber toaide in processing. For example as previously described, several fans124 may be included within the chamber 104 to facilitate circulation ofthe environment such as heated air or gas, reactive and/or inert gases,as well as other environmental gases such as steam. The fans 126 areeffective to provide a more even temperature profile or environmentwithin the chamber 104. The fans 124 may be connected to the fan shaft126 by any suitable means such as keys. The fan shaft 126 extendsthrough the bottom plate 110 of the apparatus 100 where it connects to adrive assembly 140, such as through a gear reducer at its lower end. Thefans 124 may be powered such as by motor, or by other power sources suchas hydraulic, steam, gas, or the like. As the drive assembly 140 causesthe shaft 126 to rotate, the fans 124 rotate in turn, thus pushing theinternal environment within the chamber 104 across the exposed sewagesludge on each of the trays 112.

The sewage sludge is processed within the apparatus 100 by, for example,heated air or gas distributed to the processing chamber 104 through amanifold system 142 in fluid communication with a heat exchanger 144 andan air intake fan 146. The manifold system 142 is coupled to thesidewall 106 of the housing 102. The manifold system 142 includes aconditioned air inlet 148 and at least one conditioned air outlet 150.As shown in FIG. 2, in accordance with one embodiment of the presentinvention, the apparatus 100 includes a manifold system 142 includingthree spaced apart conditioned air outlets 150. The outlets 150 arearranged at predetermined locations opposing the trays 112 between thetop plate 108 and bottom plate 110 of the apparatus 100. The particularnumber of outlets 150, their arrangement and location relative to thetrays 112, may be varied depending upon the operating conditionsintended within the processing chamber 104 for the treatment of sewagesludge therein.

In the preferred embodiment, each of the outlets 150 may include acontrol damper 152 for controlling the volume of heated air beingdischarged by the manifold system 142 into the processing chamber 104.Controlling the individual dampers 152 allows for a controllabletemperature profile within the processing chamber 104. Each of thedampers 152 may be manually controlled, or in the alternative, beconnected to a microprocessor base control system 153 having temperaturefeedback from thermal couples placed within the apparatus 100. Thecontrol system 153 can also control the temperature of the heated airfrom the heat exchanger 144 and operation of the intake fan 196,including internal fans 124. The control system 153 may be connected toa wired or wireless network e.g., the internet.

With reference to FIG. 3, the manifold assembly 142 further includes aninternal elongated duct 154 within the chamber 104 in communication witheach of the outlets 150. The duct 154 includes an end wall 156 generallyarranged parallel to the inner surface of the sidewall 106. The duct 154is open along one side edge forming an elongated opening 158 arrangedtransverse to the sidewall 106. In the preferred embodiment, theelongated opening 158 is arranged perpendicular to the sidewall 106, andparallel to the flow direction of the heated air discharged through theoutlets 150.

In operation, heated air from the blower 146 is heated by the heatexchanger 144 and discharged into the manifold system inlet 148. Inturn, the heated air passes through the manifold system 142 andultimately through the air outlets 150 under the control of the dampers152, if provided. The conditioned air enters the duct 154 in a directionalong the diameter 160 of the apparatus 100 or generally perpendicularto the sidewall 106. Upon entering the duct 154, the direction of theheated air is redirected to be discharged through the opening 158,generally parallel to the inner surface of the sidewall 106 andperpendicular to the diameter 160 of the apparatus 100. Thus, the heatedair from the manifold system 142 is discharged into the processingchamber 104 in a direction generally parallel to the sidewall 106, andnot directly onto the opposing trays 112. This allows the incomingheated air to be blended internally within the processing chamber 104with the internal conditioned air to provide a more uniform temperaturewithin the processing chamber. This subjects the sewage sludge beingprocessed on each of the trays 112 to a more uniform temperaturedistribution than what otherwise might occur if the heated air wasdischarged directly from an outlet 150 onto an opposing tray.

As previously described, the apparatus 100 may include a plurality oflevelers 138 positioned in operative association with the trays 112.Discharging heated air from the manifold system 142 into contact withthe levelers 138 can result in the heated air having a turbulent flowpattern which might result in less desirable drying attributes forsewage sludge on associated trays 112. To overcome this issue, inaccordance with a preferred embodiment of the present invention, one ormore barriers 162 are arranged obstructing certain portions of theelongated opening 158 formed in the duct 154. In general, the barriers162 are arranged in alignment with and opposing each of the levelers 138within the processing chamber 104. In addition, the barriers 162 may bepositioned opposing other internal obstructions within the processingchamber 104 for a similar purpose.

The sewage sludge being supplied to the apparatus 100 may undergovarious processing conditions within the chamber 104. For example, thesewage sludge may initially be subject to drying within an upper portionof the chamber 102 encompassing a plurality of trays 112. The sewagesludge is further processed in a lower portion of the processing chamber104 in one or more trays 112 to destroy or reduce the amount ofpathogens in the dried sewage sludge. Typically, the processing of thesewage sludge within the chamber 104 will be under a selected gasenvironment. By way of example, various gas environments may includeheated air, stream, inert gases, other gases and the like. It is alsocontemplated that internal heating rods or tubes may be incorporatedinto the processing chamber 104 as a source of heat for processing thesewage sludge.

The apparatus 100 may be modified to include additional features,systems, and equipment as dictated by the process being performed orother considerations. For example, many sewage sludges are treated usinga variety of digestion techniques, the purpose of which is to reduce theamount of organic matter and the number of disease-causingmicroorganisms present in the solids. The most common treatment optionsinclude anaerobic digestion, aerobic digestion, and composting.

Anaerobic digestion is a bacterial process that is carried out in theabsence of oxygen. The process can either be thermophilic digestion inwhich sludge is fermented in tanks at a temperature of 55° C. ormesophilic, at a temperature of around 36° C. Anaerobic digestiongenerates biogas with a high proportion of methane (including carbondioxide and hydrogen sulfide) that may be used to both heat the tank andfor other on-site processes. Sufficient energy can be generated in thisway to produce all or a portion of the heat required for processing thesewage sludge in the apparatus 100.

The treatment of sewage sludge which may contain one or more pathogensusing the apparatus 100 will now be described. In the preferredembodiment, sewage sludge is dewatered prior to being fed to theapparatus 100. As previously described, the sewage sludge may be treatedby preliminary treatment, primary settlement, and secondary treatment.In the preferred embodiment, and by way of one example only, sewagesludge having a dry solids content from about 30% to about 40% by weightis fed to the inlet 120 of the apparatus 100 by any suitable means, forexample, by a screw feeder. It is to be understood that the sewagesludge being fed to the apparatus 100 may have other dry solids contentfor processing in the apparatus 100. The sewage sludge is processedwithin the apparatus 100 to increase the dry solids content at theoutlet 122 to greater than about 90%, more preferably greater than 92%,and in accordance with the preferred embodiment, in the range of about96% to 98%. Stated differently, the processed sewage sludge from theapparatus 100 by way of example, will have a dry solid content of atleast 90%, preferably above 92%, and more preferably about 98% drysolids.

Heated air is supplied to the processing chamber 104 by means of theintake fan 146 and heat exchanger 144. The air may be heated in the heatexchanger using steam, combustion gases, or electric heat within thechamber 104 as previously noted. By way of example only, the heated airdischarged into the processing chamber 104 through the conditioned airoutlets 150 is controlled to an inlet temperature in the range of about150°-175° C. Varying temperatures within the processing chamber 104 toprovide a uniform or controlled distribution can be controlled using thedampers 152. In the preferred embodiment, the temperature within theprocessing chamber 104 is controlled within the range of from about120°-150° C. However, it is to be understood that these temperatures areonly exemplary, and that other temperatures are contemplated.

In general, the temperature near the bottom of the processing chamber104 is often hotter than the temperature near the top of the processingchamber where the sewage sludge has a higher moisture content. Thetemperature within the processing chamber 104 is controlled such thatthe sewage sludge is preferably maintained below its ignition orsmoldering temperature to prevent the formation of embers within thedried sewage sludge. The formation of embers can be a fire hazard uponstoring the dried processed sewage sludge. The embers, if present, canresult in the dried sewage sludge catching fire. As the sewage sludge isheated within the processing chamber 106, water vapor and any flue gasescreated from the heat treatment of the sewage sludge is discharged fromthe apparatus 100 by exhaust discharge 164.

After revolution of the top tray 112, the sewage sludge is wiped bymeans of the wiper 118 onto the next lower tray, where it is mixed,leveled by leveler 138, and then after revolution of the tray, is wipedto the next lower tray where the operation is repeated. In this manner,the sewage sludge cascades downwardly through the processing chamber 104from one tray 112 to the next underlying tray. As previously described,the trays may be stationary, and the wipers 118 may be rotated to affectdischarge of the sewage sludge through openings 116 within the trays.The trays 116, by being contained within the enclosed processing chamber104, are subject to the heated air or gases that are circulated by theinternal fans 124. This approach to drying of the sewage sludge enablesan exceptionally gentle handling of the sewage sludge withoutback-feeding. Combined with the precisely controlled and uniformtemperature environment as thus far described, the apparatus 100produces a consistently odorless sized granular with little dust orfines in a manner that ensures against material smoldering or ignitionby not forming embers.

Another approach to preventing fires within the apparatus 100 is the useof an anaerobic gas such as nitrogen. However, if the dried sewagesludge gets overheated even under an inert gas, it can catch fire whenexposed to air upon discharge from the apparatus. By controlling thetemperatures within the processing chamber 104 as noted hereinabove, theapparatus 100 eliminates the need for the use of nitrogen, while at thesame time, avoiding fires and odors that are discharged from theproduct. In this regard, the apparatus 100 prevents the generation ofodor by ensuring that the sewage sludge is not overheated or baked, andthat neither the processed sludge nor the trays 112 are exposed tosuperheated hot air. However, it is contemplated that nitrogen may beused in conjunction with the above described process. It is alsocontemplated that the apparatus 100 may also be operated under a slightnegative pressure, e.g., vacuum in the range of from about 0.01-0.04inches water, that addresses the issue of dust formation and controllingodors discharged from the apparatus.

Before discharge from the apparatus 100, the dried sewage sludge in theupper trays 112 is processed to destroy and/or to reduce the level ofpathogens in complying with the EPA requirements as noted hereinabove,e.g., Part 503 Rule of the above EPA regulations. The describedtreatment process for sewage sludge requires that the sewage sludge betreated at a predetermined temperature and residence time. To satisfythe temperature and residents time requirements, the EPA in Part 503Rule provides a time-temperature relationship equation for use in wastetreatment facilities. By way of example, the EPA regulations requireheating the sewage sludge to a temperature in the range of 50°-80° C. orhigher for 20-30 minutes or longer, which is the standard for killingpathogens to meet Class A biosolids requirements. Preferably the sewagesludge is treated by attaining a temperature of 80° C. for 30 minutes.This temperature and residence time requirement can be achieved at leastwithin the lower trays 112 within the processing chamber 104 of theapparatus 100.

Moreover, as noted hereinabove, the processing conditions within theprocessing chamber 104 maintains the sewage sludge continuously abovethe EPA temperature requirement, while avoiding overheating of thesewage sludge and at a temperature below the ignition or smolderingtemperature to preclude the formation of embers. Thus, the sewage sludgegets exposed to the required temperature and residence time while beingprocessed through the processing chamber 104, while avoiding gettingoverheated which can potentially produce dust and embers. Prior todischarge of the sewage sludge from the apparatus 100, the lower mosttrays 112 may be used for cooling the sewage sludge prior to dischargefrom outlet 122. In the preferred embodiment, the discharged sewagesludge is cooled in a separate unit such as a cooling screw or parallelplate cooler and the like.

Referring now to FIG. 4, there is disclosed an apparatus 100 which hasbeen modified pursuant to one embodiment of the present invention. Aprocess chamber exhaust duct 166 is provided in fluid communication withthe exhaust discharge 164. The exhaust duct 166 is further in fluidcommunication with a recycled duct 168 coupled to the manifold system142. Control dampers 170, 172 may be provided within the exhaust duct166 and the recycle duct 168. By controlling the dampers 170, 172, theexhaust from the process chamber 104 can be directed to the outsideatmosphere via damper 170, or recycled back to the processing chamberthrough the control damper 172. Thus, a portion or all of the exhaustfrom the processing chamber 104 may be discharged to the atmosphere orrecycled back to the processing chamber. The recycled exhaust providesrecovered heat from the processing chamber for operation of theapparatus 100 during treatment of the sewage sludge. Optionally, acondenser 147 may condense a portion of the moisture in the exhaust, orother possible volatiles that may be discharge from the sewage sludgeduring processing. The condenser 174 may be substituted by other typesof equipment such as desiccant dryers and the like.

Referring to FIG. 5, there is illustrated an apparatus 100 constructedin accordance with another embodiment of the present invention. Thesewage sludge 176 is initially processed in an anaerobic digester 178prior to being fed into the apparatus 100 such as through a controlvalve 180. The methane gas generated within the digester 178 is fed viaa conduit 182 to a heat exchanger/burner 184. The methane gas can beignited within the burner 184 with supplemental gas supplied via gasinlet 186. The heated flue gas from the combustion can be used forheating a portion of the exhaust being recycled to the processingchamber 104 through the recycled duct 168. In addition, the heated fluegas can be fed via conduit 188 to the heat exchanger 144 for heating theincoming air via fan 146.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

The invention claimed is:
 1. A method for treatment of sewage sludgecontaining a pathogen, comprising: cascading sewage sludge containingwater and at least one pathogen between a plurality of vertically spacedapart supports within a processing chamber; heating the sewage sludgewhile cascading within the processing chamber to remove a portion of thewater within the sewage sludge thereby forming a reduced water contentsewage sludge; heating the reduced water content sewage sludge for asufficient time and at a sufficient temperature to reduce the amount ofthe at least one pathogen within the sewage sludge thereby forming atreated sewage sludge; supplying heated gas to the processing chamberfor heating the sewage sludge for removing a portion of the containedwater therein and for reducing the amount of the at least one pathogenwith the sewage sludge; and controlling the temperature of the heatedgas within the processing chamber below the ignition temperature of thesewage sludge to prevent the formation of embers therefrom.
 2. Themethod of claim 1, wherein the treated sewage sludge has a dry solidcontent of at least 90% by weight.
 3. The method of claim 1, whereinheating the sewage sludge for a sufficient time and at a sufficienttemperature to reduce the amount of the at least one pathogen comprisesheating the sewage sludge of reduced water content to a temperature inthe range of 50° C.-80° C. or higher and for a time in the range of20-30 minutes or longer.
 4. The method of claim 1, wherein thetemperature comprises 80° C. and the time comprises at least 30 minutes.5. The method of claim 1, wherein the heated gas supplied to theprocessing chamber is in the range of 150° C.-175° C.
 6. The method ofclaim 5, wherein the heated gas within the processing chamber iscontrolled within the range of 120° C.-150° C.
 7. The method of claim 1,wherein supplying the heated gas to the processing chamber furthercomprises discharging the gas into the processing chamber in a directionperpendicular to a diameter of a housing providing the processingchamber.
 8. The method of claim 1, rotating the supports while thesewage sludge cascades within the processing chamber.
 9. The method ofclaim 1, wherein the reduced water content sewage sludge comprises atleast 90% dry solids.
 10. The method of claim 9, wherein heating thereduced water content sewage sludge occurs at a temperature in the rangeof 50° C.-80° C. or higher and for 20-30 minutes or longer to reduce theamount of the at least one pathogen within the sewage sludge therebyforming the treated sewage sludge.
 11. The method of claim 10, whereinsupplying heated gas to the processing chamber occurs at temperaturerange of 120° C.-175° C.
 12. The method of claim 11, wherein supplyingthe heated gas to the processing chamber further comprises dischargingthe gas into the processing chamber in a direction perpendicular to adiameter of a housing providing the processing chamber.
 13. The methodof claim 12, wherein the heated gas comprises air.